Construction and agricultural equipment have moveable members that employ hydraulic structures including a hydraulic cylinder and piston arrangement. These structures can be controlled by one or more poppet valves that control the flow of hydraulic fluid to these structures. Some poppet valves include a control chamber connected to an inlet port through a meter-in orifice and to an outlet port through a meter-out orifice. Opening of the poppet valve is controlled by controlling fluid flow through the meter-out orifice to reduce the control pressure in the control chamber such that the inlet pressure urges a poppet of the poppet valve off a valve seat when the control pressure drops below the inlet pressure in the inlet port. The meter-out orifice is controlled by a pilot valve, which can be selectively opened by applying an electric current on an actuator connected to the pilot valve.
One of the problems associated with such poppet valve designs is that the poppet valve can be opened only when the pressure in the inlet port is higher than the pressure in the outlet port. If the pressure in the outlet port is higher than the pressure in the inlet port, the poppet valve cannot be opened. It is desirable to have a poppet valve openable in both situations.
U.S. Pat. No. 6,328,275 (the '275 patent) issued to Yang et al. discloses a pilot-operated poppet valve to control a bidirectional flow of fluid between two ports. The poppet valve disclosed in the '275 patent includes a first passage extending between a control chamber and a first port. A check valve allows fluid to flow through the first passage only in the direction from the first port to the control chamber. A second passage extends between the control chamber and the second port. Another check valve allows fluid to flow through the second passage only in the direction from the second port to the control chamber.
The system of the '275 patent may provide a bidirectional pilot operated control valve, but the system of the '275 patent employs a direct feedback mechanism, in which the maximum opening of the poppet valve is limited by the movement of the pilot poppet.
The disclosed system is directed to overcoming one or more of the problems set forth above.